The HVAC system typically consumes 70% to 85% of a building's total energy usage. Much of this energy is used to condition air, heating, cooling and dehumidification. The other consideration is indoor environmental comfort. Because of tight building envelopes and non-operable windows, outside air has to be mechanically introduced into a building per code (ASHRAE 62) to control build-up of gaseous contaminants and provide acceptable air quality. This outside air needs to be conditioned, therefore increasing demands on the HVAC system, which consumes more energy and shortens equipment life, while running up the utility bill.
The major consideration of ASHRAE's 62 ventilation code is to provide acceptable air quality, to control contaminants by dilution or ventilation. Within the 62 code, ASHRAE also makes available an option to provide an engineered solution that allows the designer to reduce the ratio of outside air to re-circulated air, which then equates to decreased load requirements for the HVAC system, resulting in reduced energy and operating costs. This procedure, named the “IAQ Procedure”, requires the designer to identify the typical contaminants that need to be controlled within the desired space and design an air cleaning strategy to control these contaminants within acceptable levels, as determined by recognized authorities. This presents a great opportunity for energy savings by reducing load demand on the HVAC system, which will result in first cost savings by equipment downsizing, and on-going energy savings due to reduced demand.
Indoor air quality in occupied spaces has been typically controlled by two methods: (1) mechanically introducing amounts of outdoor air in with the re-circulated air to dilute and control contaminants within the space; and (2) the use of filters.
The first method is the basis for the ASHRAE 62.1 standard which is titled “Ventilation for Acceptable Air Quality”. However, the disadvantage of introducing outside air is that the outside air needs to be conditioned, heated, cooled and dehumidified in order for the building to maintain a proper comfort level. This added conditioning load requires additional energy. The largest energy demand in any building is typically HVAC, and outside load typically uses the most energy of the HVAC system. Also added load causes the HVAC systems to work harder, to require more maintenance, and to wear out faster.
Filters can be used remove particles from the air stream of the HVAC system. These unwanted particles are generated in spaces and also introduced by the outside air. The original intended use of standard filters was to protect the HVAC components from dirt and debris and premature wear. However, today's filters are designed for better control of contaminants and are thicker and pleated rather than flat to increase their surface area and catch more and smaller particles. Also, increasing air exchange rates from the HVAC system requires that more air be driven through the filter and increase its efficiency. The disadvantage is that all filters will restrict airflow to some degree and make the HVAC system work harder to condition the space for comfort. The higher efficiency filters result in more airflow restriction, and as the HVAC system works harder, it consumes more energy. Also, by increasing air exchange rates to drive more contaminants through a filter to maximize its efficiency, the HVAC system must work harder and consume more energy. Filters also require continual maintenance to replace dirty loaded filters.
Many manufacturers of unitary systems, fan powered boxes, etc. have attempted to develop feasible ways to offer improved air quality with their systems, but have been unsuccessful because of airflow restriction and load demands. The present invention provides a solution to these problems.